hyperv/kvp: Fix IPv4/IPv6 address injection support.

The GUID string provided by hypervisor has leading and trailing braces,
while our GUID string does not have braces at all. Both braces should
be ignored, when the GUID strings are compared.

Submitted by: Hongjiang Zhang <honzhan microsoft com>
Modified by: sephe
MFC after: 1 week
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D7809